One type of image-forming device is equipped with photosensitive drums arranged in tandem and parallel to one another. Four photosensitive drums are typically provided for the four colors yellow, magenta, cyan, and black. The image-forming device also has an endless conveying belt disposed in contact with all photosensitive drums for conveying sheets of paper so that the sheets sequentially contact each of the photosensitive drums. Toner images formed on the photosensitive drums are transferred onto the sheet of paper conveyed by the conveying belt, forming a color image on the paper with the superposed images of each color.
Since residual toner remaining on the photosensitive drums after an image-forming operation can become deposited on the conveying belt, a cleaning member is generally provided for removing toner from the conveying belt. Toner removed from the conveying belt by the cleaning member is conveyed to a waste toner collecting unit for storage. An image-forming device that integrally provides the waste toner collecting unit with a developer cartridge has been proposed. When the developer cartridge runs out of toner, the waste toner collecting unit is replaced together with the developer cartridge.